Douglas B. Hunter

Application of Synchrotron X-ray Fluorescence Spectroscopy and Energy Dispersive X-ray Analysis To Identify Contaminant Metals on Groundwater Colloids

The objective of this study was to combine the results from SXRF and EDX to provide information about the elemental composition of individual groundwater colloids and about the identity of contaminants associated with these colloids. Because the contaminant metals in the study site came from a point source, their presence on groundwater colloids would provide elemental signatures suggesting that colloids may be important in contaminant transport. SXRF was used to detect low concentrations of contaminant metals associated with surfaces of clusters of groundwater colloids. EDX was used to detect the more abundant elements (including the geochemically important, lower atomic number elements Al and Si that are insensitive to SXRF) associated with surfaces of individual colloids. These techniques were also selected because they require only a small sample mass, about 0.01 g, which may be the total quantity of colloids recovered from 24 h of groundwater sampling. The study site was an aquifer underlying unlined seepage basins that had received wastewater containing sodium hydroxide, nitric acid, radionuclides, and numerous metals from a nuclear materials processing facility on the Savannah River Site near Aiken, SC. 12 refs., 2 figs., 2 tabs.

Comparison of acid and base leach for the removal of uranium from contaminated soil and catch-box media

Several leach solutions have been developed for the removal of uranium (U) from contaminated media such as soil and military catch-box sand used for the ballistics testing of U-containing projectiles. Leach solutions of concentrated sulfuric acid and of carbonate (with and without oxidants such as peroxides) have also been used in the mining of U from high-grade ore deposits. Many of these solutions have been used at U-contaminated environmental sites with varying degrees of success. Batch leaches with six characterized U-contaminated media and seven leach solutions were conducted. After the leach solutions were reacted with the media (five soils and a catch-box sand), the solutions were analyzed for dissolved U, Ca, Si, Fe, Mn, Pb and Cr. We study the ability of acidic, basic, acidic-oxidizing and basic-oxidizing solutions to leach U from contaminated media. The results suggest the removal efficiency of soil U for each leach solution varies with the nature of the U-contamination in the media and the medi...

In situ measurements of tetraphenylboron degradation kinetics on clay mineral surfaces by IR

An attenuated total reflectance Fourier transform infrared (ATR-IR) spectroscopic method has been developed to quantitatively measure, in situ, the surface-facilitated degradation of tetraphenylboron (TPB) in fully aquated clay pastes. Two pathways for degradation of TPB could be studied both independently and simultaneously. Surface-facilitated oxidation of TPB to diphenylboric acid (DPBA) at Lewis acid sites on clay mineral surfaces was investigated on three members of the smectite family of clays. No degradation of TPB occurred on hectorite, which contains no structural Fe. TPB degraded to DPBA on montmorillonite and nontronite. A color change in nontronite indicated the production of mixed valence Fe[sup 3+]-O-Fe[sup 2+] states and clearly demonstrates the reduction of structural iron during the course of the reaction. The degradation of TPB to triphenylboron (TriPB) at Bronsted acid sites could also be measured on aluminum-saturated clays either independently on hectorite or simultaneously to the Lewis acid reaction on montmorillonite by the ATR-IR method. First-order rate models are developed for both reactions and describe the data well. 28 refs., 4 figs., 1 tab.

Separation of Argon and Oxygen by Adsorption on a Titanosilicate Molecular Sieve

Abstract A titanosilicate molecular sieve adsorbent, Ba-RPZ-3, was synthesized and tested for its use in the separation of O2+Ar mixtures at room temperature. A clean resolution of both gases was achieved in pulse chromatographic experiments using a standard column (0.25″ OD, 3.5 grams of adsorbent). In another experiment, using a column containing 30 grams of adsorbent and a continuous O2+Ar feed at 10 cm3/min, argon breakthrough was detected more than 5 minutes before the oxygen breakthrough, and the separation was sufficiently sensitive to achieve quantitative separation of mixtures with low argon content (5% Ar). Equilibrium adsorption isotherms and isosteric heats of adsorption for oxygen and argon were found to be almost identical at room temperature. The thermodynamic selectivity was found to be mildly in favor of oxygen (∼1.1–1.2). However, the adsorption of oxygen was observed to be much faster than argon, indicating that the separation of the O2+Ar mixtures was based on the sieving properties of the adsorbent and the difference in sizes of O2 molecules and Ar atoms. This indicates that a suitably-oriented oxygen is physically smaller than argon, despite the fact that many references assume that oxygen is larger than argon.